1. Field of the Invention
The present invention relates to an impact dot print head in a printer and more particularly to an impact dot print head wherein an armature is operated using a magnetic circuit to effect printing, the magnetic circuit being formed by allowing a magnetic flux which is generated by energizing a coil wound round a core provided in a yoke, to flow through an armature spacer, etc., as well as a printer using the impact dot print head.
2. Description of Background Art
Heretofore there has been known an impact dot print head wherein an armature with a printing wire connected thereto is pivoted between a printing position and a standby position, and when the armature is pivoted to the printing position, a tip of the wire is brought into collision with recording paper to effect printing.
In a certain impact dot print head of this type, a magnetic circuit is formed around the armature to be pivoted, the magnetic circuit causing the armature to be attracted from a stand-by position to a printing position with a magnetic flux generated by a coil to effect printing.
For example, the magnetic circuit comprises a yoke having a core with a coil wound thereon to generate a magnetic flux, an armature spacer disposed near an armature at a position in contact with the yoke and not obstructing a pivotal motion of the armature, and the armature which is pivotable between the printing position and the stand-by position. Generally, the yoke is fabricated by forming, while the armature spacer is fabricated by pressing sheet metal. By fabricating the armature spacer by pressing sheet metal it is possible to reduce the armature spacer manufacturing cost.
Although the quality of the yoke fabricated by forming is stable, but that of the armature fabricated by pressing sheet metal is apt to vary.
In the conventional impact dot print head, the yoke and the armature spacer are brought into surface contact with each other, and through the contact surfaces magnetic flux is allowed to flow between the yoke and the armature spacer. However, when there occur variations in the armature quality, it is difficult to maintain a satisfactory state of contact between the armatures and the yoke.
If the state of contact between the armatures and the yoke is unsatisfactory, the magnetic flux flowing efficiency between each armature and the yoke is deteriorated and the attracting force for attracting each armature to the associated core is decreased.
Recently various measures for attaining a high printing speed and a high printing pressure have been taken, but due to the aforesaid decrease of the attractive force which is caused by the generation of leakage flux it is difficult to attain a high printing speed and a high printing pressure to a satisfactory extent.
To avoid such an inconvenience, the armature spacer is subjected to grinding after pressing to ensure a high flatness of its surface of contact with the yoke.
In the conventional printer, however, for maintaining a satisfactory state of contact between the armature spacer fabricating by pressing sheet metal and the yoke, it is necessary to subject the armature spacer to grinding after the pressing work. But the application of this grinding work results in an increase in the number of armature spacer manufacturing steps, and the manufacturing cost increases despite the adoption of the pressing work.
Since the grinding work is performed for each armature spacer, each armature spacer is apt to vary in quality. An attempt to decrease this variation results in a still higher manufacturing cost.